Effect of Precursor Solution Volume on Structural and Optical Properties of Iron Doped Titanium Dioxide Thin Films Prepared by Spin Coating

Abstract

The influence of precursor solution volume on the characteristics of containing iron-doped titanium dioxide (Fe:TiO2) thin films was examined in this work. The coatings were prepared on transparent substrates by the spin-coating method using precursor volumes between 0.5 and 2.5 mL. Following deposition, the coatings were heat treated at 450°C and analyzed using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and ultraviolet-visible (UV-Vis) spectroscopy. XRD analysis revealed the presence of both rutile and anatase crystalline phases, evidenced by reflections near 27.4° and 49° corresponding to the (110) and (200) planes, respectively. Variations in precursor volume affected the crystallographic properties of the films, with the sample prepared using 1.0 mL exhibiting the largest crystallite size and sharper diffraction peaks, suggesting improved crystal growth. Increasing the precursor volume beyond this value resulted in peak broadening, which may be associated with greater lattice imperfections and strain within the films. The FTIR results identified characteristic vibrational bands assigned to Ti-O-Ti and Ti-O-Fe linkages, confirming the incorporation of iron species into the TiO2 network. Optical characterization showed that increasing precursor volume shifted the absorption threshold toward longer wavelengths and reduced the optical band gap. This behavior can be ascribed to the creation of defect-induced energy states and oxygen-vacancy states within the material. Overall, the findings demonstrate that precursor solution volume significantly affects both the crystallographic and photonic performance of Fe:TiO2 coatings, with the 1.0 mL sample providing the most favorable combination of crystallinity and film quality.